The development of the transformer isolated forward converter has resulted in improvements in switched power supplies. This is because the forward converter costs less than the other types of transformer/isolated switching power supplies, and it is easier to design. The forward converter has evolved into the double forward converter which provides output power in the kilowatt range, and which has a faster transient response and uses smaller components than the other types of switched power supplies.
The push-pull converter is the most widely used of the switched power supplies in the prior art, although it suffers the disadvantage of collector current peaking if its transformer saturates when there is a direct current unbalance or sudden rise in load. Attempts to prevent such collector current peaking in the prior art push-pull converter has led to circuit complexities.
The forward converter has output capabilities comparable with those of the push-pull converter, but it does not have the problems of direct current unbalance in the transformer core which are encountered in the push-pull converters. This is because transistor conductivity in the forward converter occurs only once for each cycle, and the core is reset during the off time of each cycle to a predictable flux level. In addition, there is less flux peaking in the output transformer of the forward converter than in the push-pull converter, and there is no interaction between the magnetizing and load currents. Moreover, the double forward converter utilizing two transformers is suitable for high power applications.
The forward converter and the double forward converter are described in detail in an article in Electronics, Feb. 2, 1978 entitled "Low Cost Forward Converters Ease Switching Supply Design" by Kees van Velthooven and Hugo Koppe.